Unless otherwise indicated herein, the approaches described in the background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in the background section.
Audio amplifiers are well known and are used extensively to amplify audio signals. Designing an audio amplifier generally requires balancing two competing concerns. The first concern is fidelity, which relates to the accuracy with which the audio amplifier reproduces the sounds contained in the audio signal. The second concern is power efficiency, which relates to the power consumption of the audio amplifier under various operating conditions.
FIG. 1 is a block diagram of an amplifier 200, such as a class D amplifier. Amplifier 200 may be configured to amplify a set of analog signals for output of the amplified analog signals on a load 210 (i.e., a speaker). More specifically, amplifier 200 may include a signal generator 220 that may be configured to process received digital signals (Dinp, e.g., digital audio signals) and output first and second pulse width modulated (PWM) signals 225a and 225b having different pulse widths, which encode the digital signals. Signal generator 220 may be a Digital Signal Processor (DSP) and may include various circuits, such as a sigma-delta circuit with a subsequent pulse width modulator, for processing the received digital signal and generating the first and second Pulse Width Modulated (PWM) signals. First PWM signal 225a may be output on a positive output 230a and second PWM signal 225b may be output on a negative output 230b. An output stage 235 of the DSP may be configured to transfer either the first PWM signal 225a from positive output 230a onto an output 240 or the second PWM signal 225b from negative output 230b onto output 240. Positive and negative signals applied to switches 245a and 245b place either the first PWM signal or the second PWM signal onto output 240. A pull-up current source 250a may be coupled to positive output 230a and a pull-down current source 250b may be coupled to negative output 230b. Output 240 may be coupled to an input resistor 255 for converting the voltages of the first and second PWM signals to a PWM current signal (Ipwm).
Amplifier 200 includes an integrator 260, which may include a plurality of amplifiers, and is configured to integrate the difference between Ipwm the feedback current (Ifb) of a feedback signal. The result of the integration is provided by integrator 260 to a comparator 265.
The output of the comparator is provided to a one shot circuit 270, which controls an output stage 275 via a set of control signals. A feedback voltage is fed back from the output stage through a feedback resistor 280, which converts the feedback voltage to feedback current Ifb. As described above, the Ifb is fed back into integrator 260, which integrates the difference between currents Ipwm and Ifb. Integrator 260 is also configured to integrate the current accumulated by integration capacitor (Cint) 285, which integrates Ipwm.
For numerous applications of amplifier 200, the circuits to the amplifier operate at relatively high frequency and consume a relatively large amount power. For example, comparator 265 is a relatively high-frequency circuit that consumes a relatively large amount of power. In a variety of devices, such as handheld-mobile devices that use small rechargeable batteries, these relatively high power circuits of an amplifier can cause the charge stored on a battery to be consumed relatively quickly, which is generally not desirable.
Therefore, new amplifiers are needed that have relatively high-power efficiency, and new methods of operation of amplifiers are needed that provide for relatively reduced power consumption, for example, to extend the time a handheld-mobile device may operate between battery charges.